1. Field of the Invention
The present invention provides a light uniform device for a digital light processing (DLP) projection system.
2. Descriptions of the Related Art
Projectors have become popular and more commonly used as more diversified projectors are coming onto the market. Accordingly, increasingly heightened requirements are imposed on the imaging quality of the projectors. Generally, a projection system primarily comprises an illumination subsystem and an imaging subsystem. In this industry, special emphasis has been put on improving the arrangement reliability of components, shrinking the overall volume and increasing the light source efficiency in the illumination subsystem to enhance the imaging brightness in the back-end imaging subsystem.
The illumination subsystem comprises a light source module, a lens and a light uniform device. To improve the imaging brightness, most conventional digital light processing (DLP) projection systems utilize a plurality of light source modules to provide ample light. As light propagates by scattering from the light source modules, a light source of non-uniform distribution results, which renders light illuminated on an imaging component of the projection system also non-uniform. Therefore, a reflecting cover is typically designed to reflect the scattered light towards a predetermined light path, and the light is then uniformed by a light uniform device to form a bright square region to be projected onto the imaging component. Thus, the imaging device can be illuminated by adequate uniform light to form a projection image. In practice, the light uniform device is an integrator, while the imaging component is a digital micromirror device (DMD). It should be noted that the bright region must cover the entire DMD completely in order for the DMD to reflect a complete projection image.
The projection image from the DMD is projected towards a projection lens and then forms an upstanding image on a screen for the user to watch. As required by some specifications or design requirements, the DMD needs to be installed at a certain deflection angle. This causes the DMD to be deflected with respect to the bright region to an extent that some portions of the DMD fall outside the range covered by the bright region, thereby resulting in an incomplete projection image. In this case, the bright region must be deflected along with the DMD by the same angle in order for the DMD to be covered completely by the bright region, thus a complete projection image is formed.
In more detail, as shown in FIG. 1, if the light uniform device 1 were not deflected along with the DMD, a bright region X (depicted in FIG. 1 by oblique lines) formed by light 12 emerging from the light uniform device 1 would fail to completely cover the DMD D, making it impossible to form an image properly. To have the bright region X completely cover and uniformly illuminate the DMD D but with minimal area, the light uniform device 1 must be installed in such a way that it is deflected along with the DMD D by a certain angle. In such a case, to obtain the maximum luminous flux in the light uniform device, the illumination subsystem as a whole must be deflected by this angle accordingly, which causes the plurality of light source modules in the illumination subsystem to be inclined at an angle.
However, the inclination of the plurality of the light source modules not only leads to a complex and bulky design of the projection system's internal structure, but also causes poor heat dissipation performance because the inclined light source modules prevent the cooling fan from effectively generating a smooth convection flow field. Moreover, as the hot air tends to rise above, massive waste heat generated by the light source modules will accumulate above the inclined lamp bulbs and the reflecting cover at the front ends thereof. After a period of operation, the heat accumulated by the high temperature tends to shorten the service life of the bulbs and cause damage to the light source modules.
To deflect the light emerging from the light uniform device, another practice is to use a relatively complex relay lens at the rear end of the light uniform device to guide the light to cover the DMD completely in a uniform way. There is then no need to deflect the light uniform device and avoids the shortcomings arising from disposing the light source modules at an inclined angle. Unfortunately, this practice adds to both structural complexity and cost of the projection system.
Thus, in current DLP projection systems, as limited by the requirements to the plurality of light source modules, the light source modules must be installed at an inclined angle to coordinate with the deflected integrator. This leads to additional complexity of the structural design, increased overall volume and poor heat dissipation performance of the light source modules; all of which make such a solution undesirable. On the other hand, the practice of using an additional relay lens to obviate the need of inclining the light source modules is costly, degrades the optical efficiency due to an overlong light path, and also causes increased volume of the projection system due to an overly complex structural design and too many optical components.
Accordingly, efforts still have to be made in the art to provide a more effective imaging light source for a projection system that can obviate the shortcomings arising from deflecting the light source modules while still keeping the cost under control and reducing the overall volume of the projection system.